Giuliani, who is acting as the president's personal attorney, during an interview Monday with Fox Business first said reports that Trump threatened to cut aid was “a false story,” but then backtracked when pressed.

BARTIROMO: Did the president threaten to cut off aid to Ukraine?GIULIANI: No, no. That was a false story. BARTIROMO: 100 percent?GIULIANI: Well I can't tell you if it's 100% percent. pic.twitter.com/ApBGsK6kZz

The Wall Street Journal on Friday reported that Trump repeatedly pressured Ukraine President Volodymyr Zelensky to investigate Biden's son Hunter Biden, who had been doing work in Ukraine.

Biden is running for the Democratic presidential nomination and is seen as the front-runner. Polls have shown him ahead of Trump in head-to-head match-ups. No evidence has emerged of any impropriety on the part of the former vice president, even as Trump has made calls for him to be investigated.

The Journal reported that its source said the issue of U.S. military aid to Ukraine didn't come up in the call, but lawmakers are now focused on whether there was any connection between aid and the pressure on Zelensky.

Trump has acknowledged discussing Biden and the investigation with Zelensky but has repeatedly said he did nothing wrong while dismissing Democratic criticisms.

She did say the matter needed to be handled immediately, noting a whistleblower had brought up the matter and the the Justice Department's inspector general had labeled it an urgent matter.

The contents of the whistleblower complaint have not been revealed to Congress, which is another issue that has rankled Democratic lawmakers. Pelosi has joined Democrats in calling for the complaint to be released to Congress.